Controlling the Product Selectivity of Peracetic Acid-Mediated Oxidative Lignin Depolymerization via a Deep Eutectic Solvent.

Developing a selective lignin depolymerization process remains a daunting challenge due to lignin's inherent structural heterogeneity and chemical complexity. This study used a novel deep eutectic solvent (DES) extraction to produce oligomeric lignin with controlled structural characteristics (narrow size distribution, lower molecular weight) and further subjected it to oxidative depolymerization using peracetic acid as an oxidant. Oxidation of lignin resulting from lactic acid/pyrazole and choline chloride/lactic acid extraction produces phenolic acids (Ph-COOH) and dicarboxylic acid (DCA) as significant products. Our results show that the judicial choice of DES during extraction plays a critical role in determining the lignin chemical structure, which follows different oxidation pathways and results in different product selectivities. The generalization of this concept has been established with two different parent lignins, e.g., Douglas fir (D.fir) and wheat straw (WS). The overall process showed that the novel DES extraction not only provides a sustainable pathway for high-purity lignin generation but also could be used as a tool to produce high-value products selectively upon its oxidation, thus improving the overall lignin biorefinery process.